1. Field of the Invention
The present invention relates to a method and apparatus that provides more accurate and time efficient antenna pointing for a satellite receiver antenna dish. More particularly, the present invention relates to an aperture cover that is placed over an opening of a feed horn to block some of the radiation coming into the feed horn such that the amount of power coming into the feed horn can be controllably varied and measured to determine the error angle and direction through which the satellite dish needs to be turned to achieve optimum reception from a geo-synchronous satellite. This invention is applicable for use with other fixed location microwave sources.
2. Description of the Related Art
Conventional methods of pointing a satellite receiver antenna dish to optimally receive signals from a geo-synchronous satellite involve monitoring received signal strength as the satellite dish is turned on its mount and estimating the optimum pointing from the changes in the signal strength meter reading. This is also known as xe2x80x98peakingxe2x80x99 the signal. For example, the satellite receiver antenna assembly can provide a feedback voltage from the receiver to be measured with a voltmeter or other signal strength indicator device. The signal strength indicator presents the power received by the antenna feed and is used to show the receive signal strength. In existing satellite receiver/transmitter embodiments, the value of the signal strength falls as the dish is pointed toward the source and rises as it is moved away from the signal source and past the direction of optimum signal strength. These single datum methods do not indicate the direction to which the antenna dish should be pointed to achieve optimum signal strength, nor what angle the antenna dish must be turned in order to achieve optimum signal strength. Thus, trial and error is required in conventional systems to point a satellite dish so as to achieve maximum signal strength from a geo-synchronous satellite. In addition, existing systems for pointing satellite antennas are not likely to achieve the stringent pointing tolerances (e.g.,  less than 0.2 degrees) that can be required for a broadband, multimedia satellite communication system with terminals employing a small antenna size.
A need therefore exists for a method and an apparatus that provides fast and accurate pointing of a satellite dish to achieve optimum reception from a geo-synchronous satellite.
It is therefore an object of the present invention to provide a method and an apparatus that efficiently and accurately point a satellite receiver antenna dish to optimally receive signals from a geo-synchronous satellite.
It is also an object of the present invention to provide a method and apparatus that enable a user to quickly determine the direction and the angle the antenna dish must be turned in order to receive the optimum signal strength from a geo-synchronous satellite.
It is a further object of the present invention to find the pointing direction in two dimensions for optimum reception using a two-step approach whereby the dish is displaced in a first direction (e.g., azimuth) based on a first set of measurements, and then displaced in a second direction orthogonal to the first direction (e.g., altitude) based on a second set of measurements to receive optimum signal strength.
It is yet another object of the present invention to find the two dimensional pointing correction for optimum reception using a one-step approach whereby only one larger set of measurements is taken to adjust the antenna dish to receive optimum signal strength from a geo-synchronous satellite both with respect to azimuth and altitude.
These and other objects are substantially achieved by providing an aperture cover that is configured to be removable and is attached to a collar on the feed horn of a satellite antenna receiver to partially cover the feed horn opening and therefore to partially block radiation from entering the feed horn. The aperture cover can be adjusted to cover any fraction of the feed horn opening to partially block different amounts of radiation from entering the feed horn. In one embodiment, two sets of measurements are taken and two dish movements are used to determine the optimum pointing angle of the satellite receiver antenna dish. The first set of measurements is started with the aperture cover covering one side of the feed horn opening and then is completed by rotating the aperture cover to the opposite side of the feed horn opening. The differences in these signal strength measurements determine how far and in which direction the dish should be turned. The same process is repeated in a direction orthogonal to the first set of measurements and the dish is then moved in the orthogonal direction to achieve optimum reception. This embodiment can be used on systems with circular or rectangular feed horn openings.
A second embodiment of the present invention is useful for antennas with feed horns having circular openings. A reference power measurement is first made with no aperture cover blocking the feed horn. Then, at least three measurements are taken of power received by the feed horn with the aperture cover partially covering the opening of the feed horn at equally spaced angular intervals. Between each of these measurements, the aperture cover and collar are rotated with respect to the feed horn opening by an angle of 360 degrees divided by the number of measurements taken. From these measurements, an error vector is determined to allow a single adjustment to achieve optimum power reception to a geo-synchronous satellite or fixed microwave source. The angle of the error vector is a mathematical average of the complex coordinates of data angle and signal quality measurements collected in the second embodiment. The magnitude of the error vector is proportional to the range of signal quality estimates in the data collected in the second embodiment.